[Insight-users] use of transform with itk volume

[J. Van Dalen]

Dear Luis,

On Wed, 27 Nov 2002, Luis Ibanez wrote:
> 
> Hi Jorn,
> 
> It shouldn't be necessary to use the
> ChangeInformationImageFilter on the
> registration framework.
> 
> What is the type of transform that is
> recovered from the image file ?
> 
> Is it like an Affine transform ?
> 
> Are the spacing and origin of the images
> specified independently or are they
> included in the transform ?
> 
> I would suggest you to read the images
> from the files and if the spacing and origin
> are specified independently of the transform,
> make sure that they are passed consistenlty
> to the itkImage.

Okee, but I only succeed in doing this for some specific
images (eg CT or PET). Eg when I have an image with the following 
initial transformation (indextophysical transform):
0.78 0 0 -206.61
0 0.78 0 -348.61
0.00 0.00 8.00 79.50
0.00 0.00 0.00 1.00
Then the spacing is given by (0.78,0.78,8.00) and the
origin by (-206.61,-348.61,79.50). Now, I can use
SetSpacing and SetOrigin as you suggested.

However, when I have the following initial (=indextophysical) transform 
(eg from a MRI):
0.78 0.00 0.00 -85.13
0.00 0.76 0.67 -90.17
0.00 0.18 -2.92 29.36
0.00 0.00 0.00 1.00
then I do not know what the spacing is (due to a present rotation).
What to do? I want to connect this initial transform to the
image, but even if I would be able to subtract both the spacing
and origin from this, I would still have to take into account the 
present rotation.

Regards,
Jorn.